I actually prefer Purging Flames to Heat Wave. Enough decks, especially the aggressive Mailice Demon, make use of their graveyards that it is nice to have a way that clears it out. In addition, the point removal in this deck is usually good enough to knock out early threats to make the Purging Flames deal at least a couple damage. And best of all, it leaves your Soloists alone to help you keep ramping.
I also second earlier mentions of Starsphere. In monoruby decks, there is no worry about getting three threshold before you can cast the Wrath of Zakiir, but the benefit from Starspheres are awesome in this deck when using Benvolio's power or The Crowd Roars.
Lastly, Syyn (the artifact dragon) is also great in this deck. He synergizes with Wrath of Zakiir (what with being a dragon), he often removes burn from the top of your deck for extra smashiness, and there is the once-in-lifetime glorious moment of removing a Wrath of Zakiir with his ability that you will be able to cast for free each turn for the remainder of the (extremely short at this point) game.
Good points on the Syyn, I'll have to try and work that in. Not sure about the Purging Flames though. I'll give it a try, but Heat Wave has been good to me, even if it does kill my Soloists.